1. Field of the Invention
The present invention relates to a process for preparing organochlorosilanes and more particularly, to the process for preparing organochlorosilanes of formula I by a dehydrohalogenative coupling of hydrochlorosilanes of formula II with organic halides of formula III in the presence of quaternary phosphonium salt as a catalyst to provide better economical matter and yield compared with conventional methods, because only catalytic amount of phosphonium chloride is required and the catalyst can be separated from the reaction mixture and recycled easily,
wherein R1 represents hydrogen, chloro, or methyl;
X represents chloro or bromo;
R2 is selected from the group consisting of C1-17 alkyl, C1-10 fluorinated alkyl with partial or full fluorination, C2-5 alkenyl, silyl containing alkyl group represented by (CH2)nSiMe3-mClm wherein n is an integer of 0 to 2 and m is an integer of 0 to 3, aromatic group represented by Ar(Rxe2x80x2)q wherein Ar is C6-14 aromatic hydrocarbon, Rxe2x80x2 is C1-4 alkyl, halogen, alkoxy, or vinyl, and q is an integer of 0 to 5, haloalkyl group represented by (CH2)pX wherein p is an integer of 1 to 9 and X is chloro or bromo, and aromatic hydrocarbon represented by ArCH2X wherein Ar is C6-14 aromatic hydrocarbons and X is a chloro or bromo;
R3 is hydrogen, C1-6 alkyl, aromatic group represented by Ar(Rxe2x80x2)q wherein Ar is C6-14 aromatic hydrocarbon, Rxe2x80x2 is C1-4 alkyl, halogen, alkoxy, or vinyl, and q is an integer of 0 to 5; and
R4 in formula I is the same as R2 in formula III and further, R4 can also be (CH2)pSiR1Cl2 or ArCH2SiR1Cl2, when R2 in formula III is (CH2)pX or ArCH2X, which is formed from the coupling reaction of X-(CH2)p+1-X or XCH2ArCH2X with the compounds of formula II; or
when R2 and R3 are covalently bonded to each other to form a cyclic compounds of cyclopentyl or cyclohexyl group, R3 and R4 are also covalently bonded to each other in the same fashion.
2. Description of the Prior Art
Organochlorosilanes are useful starting materials for silicones. In 1969, Benkeser and co-workers reported that benzyl chloride and benzal chlorides could be silylated with trichlorosilane-tertiary amine 1:1 mixture to give the corresponding trichlorosilyl substituted products by the dehydrochlorinative coupling reaction (Benkeser, R. A.; Gaul, J. M.; Smith, W. E. J. Am. Chem. Soc. 1969, 91, 3666).
In 1975, Furuya and Sukawa reported allyltrichlorosilane could be prepared in high yield by a coupling reaction of allyl chloride with a 1:1 mixture of trichlorosilane and tertiary amine in the presence of copper chloride as a catalyst (Furuya, N.; Sukawa, T. J. Organometal. Chem. 1975, 96, C1).
Recently, Corriu and co-workers reported that the reaction of chloroform with trichlorosilane in the presence of excess tributylamine gave bis(trichlorosilyl)methane and tris(trichlorosilyl)methane (Corriu, R. J. P.; Granier, M.; Lanneau, G. F. J. Organometal. Chem. 1998, 562, 79).
The dehydrochlorinative coupling reaction is a novel method of forming silicon-carbon bonds and useful for the synthesis of organosilicon compounds. Although the dehydrochlorinative coupling reaction of activated alkyl chlorides such as benzyl chloride or allyl chloride have been reported, the coupling reaction of unactivated alkyl chlorides with trichlorosilane has never been reported.
In the previously reports, tertiary amine was used in excess, more than the stoichiometric amount respect to alkyl chloride. The tertiary amine used is a hydrogen chloride scavenger rather than a catalyst. Since the ammonium salt obtained from the tertiary amine and hydrogen chloride has to be neutralized to recycle the amine, it would be too costly to be utilized on a large scale in industry.
It is necessary to find a way to reduce the usage of the amine or find another effective catalyst to apply the coupling reaction for industrial purposes. The present inventors have discovered that a coupling reaction of alkyl halides and hydrochlorosilanes in the presence of tertiary phosphines as a catalyst proceeded to give the corresponding coupled products in good yields by liberating hydrogen halide as a gas at reaction temperatures about 150xc2x0 C. (Korean Patent Application Number 99-13006(Apr. 13, 1999)). The dehydrohalogenative coupling reaction can be applied to not only the activated alkyl halides such as benzyl chloride or allyl chloride, but also to the unactivated alkyl halides such as n-alkylhexyl chloride or haloalkyl substituted organosilicon compounds. Later the present inventors also discovered that the reaction proceeded to give the coupling products in the presence of tertiary amine as a catalyst instead of tertiary phosphine. However, this reaction gave a little lower yield compared with the tertiary phosphine catalized reaction(Korean Patent Application Number 2000-13090(Mar. 15, 2000)).
Although the above processes required only catalytic amount of tertiary phosphine or tertiary amine and are more economically feasible compared with the previous reports, tertiary phosphine and tertiary amine also form complexes with the byproduct of hydrogen chloride and the reactant of alkyl chloride. The complexes have to be neutralized to recycle the catalyst. To solve this problem, we tested many other catalysts and finally found that quaternary phosphonium salts are good catalyst and gave excellent yields.
It is an object of the present invention to provide new catalysts of quaternary phosphonium salts for the coupling reaction of alkyl halides and hydrochlorosilanes. The quaternary phosphonium salts will not form complexes either with the byproduct of hydrogen chloride or the reactant of alkyl chloride. This will make the separation of the catalyst from the reaction mixture easier and the process more economically feasible for a large scale in industry, because it will not necessary to neutralize the catalyst to recycle.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
The present invention relates to processes for preparing the compounds of formula I which comprise a dehydrohalogenative coupling of hydrochlorosilanes of formula II with organic halides of formula III in the presence of quaternary phosphonium salt as a catalyst,
wherein R1 represents hydrogen, chloro, or methyl;
X represents chloro or bromo;
R2 is selected from the group consisting of C1-17 alkyl, C1-10 fluorinated alkyl with partial or full fluorination, C2-5 alkenyl, silyl containing alkyl group represented by (CH2)nSiMe3-mClm wherein n is an integer of 0 to 2 and m is an integer of 0 to 3, aromatic group represented by Ar(Rxe2x80x2)q wherein Ar is C6-14 aromatic hydrocarbon, Rxe2x80x2 is C1-4 alkyl, halogen, alkoxy, or vinyl, and q is an integer of 0 to 5, haloalkyl group represented by (CH2)pX wherein p is an integer of 1 to 9 and X is chloro or bromo, and aromatic hydrocarbon represented by ArCH2X wherein Ar is C6-14 aromatic hydrocarbons and X is a chloro or bromo;
R3 is hydrogen, C1-6 alkyl, aromatic group represented by Ar(Rxe2x80x2)q wherein Ar is C6-14 aromatic hydrocarbon, Rxe2x80x2 is C1-4 alkyl, halogen, alkoxy, or vinyl, and q is an integer of 0 to 5; and
R4 in formula I is the same as R2 in formula III and further, R4 can also be (CH2)pSiRCl2 or ArCH2SiR1Cl2, when R2 in formula III is (CH2)pX or ArCH2X, which is formed from the coupling reaction of X-(CH2)p+1-X or XCH2ArCH2X with the compounds of formula II; or
when R2 and R3 are covalently bonded to each other to form a cyclic compounds of cyclopentyl or cyclohexyl group, R3 and R4 are also covalently bonded to each other in the same fashion.
The present invention is described in detail as set forth hereunder.
The coupling reaction of hydrochlorosilanes with organic halides in the present invention can be carried out in most organic solvents such as toluene, hexane, tetrahydrofuran, and acetonitrile, but it also proceeds in neat condition. After sealing the reaction tube with a stainless steel stopper, heating and stirring may be applied for a certain period of time, generally 1 hr to about 48 hours, to complete the reaction. The reaction is carried out at a temperature from 10xc2x0 C. to 250xc2x0 C., preferably 130xc2x0 C. to 200xc2x0 C.
In a typical preparation, hydrochlorosilanes represented by formula II, organic halides of formula III, solvent, and quaternary phosphonium salt are placed all together in a sealed stainless steel tube under inert atmosphere. The amount of hydrochlorosilane of formula II used is equivalent or more, preferably 2 to 5 folds, relative to the amount of the compounds of formula III. Quaternary phosphonium salt is used as a catalyst in an amount sufficient to catalyze the reaction, generally, 1 to 100 mol %, preferably 3 to 15 mol %, relative to the mole of the compounds of formula III.
After completion of the reaction, hydrocarbon solvents are added to the product mixture to precipitate out the catalyst. The catalyst is filtered and recovered for recycling. The products are distilled under atmospheric pressure or vacuum. It has been reported that when organic phophonium salt immobilized on silicone resins, silica, or zeolite is used, the recovery of the catalyst is more convenient and easier for recycling (Jung, I. N.; Cho, K. D.; Lim, J, C; Yoo, B. R., U.S. Pat. No. 4,613,491).
The chlorosilanes represented by formula II used in this invention may be trichlorosilane, methyldichlorosilane, and dichlorosilane. The organohalogen compounds represented by formula III may be 1-chlorooctane, 1-chloro-3,3,3-trifluoropropane, (chloromethyl)trichlorosilane, (chloromethyl)dichlorosilane, (chloromethyl)trimethylsilane, (3-chloropropyl)trimethylsilane, allyl chloride, allyl bromide, crotyl chloride, benzyl chloride, 4-fluorobenzyl chloride, 4-chlorobenzyl chloride, 4-methoxybenzyl chloride, 4-phenylbenzyl chloride, diphenyl-1-dichloromethane, 1-chloroethylbenzene, cyclopentyl chloride, 2-chlorobutane, isopropyl chloride, dichloromethane, 1,2-dichloroethane, 1,3-dichloropropane, 1-bromo-3-chloropropane, 1,4-dichlorobutane, and 1,4-bis(chloromethyl)benzene.
The catalyst of quaternary phosphonium salts may be represented by the following formula IV,
PRxe2x80x34Xxe2x80x2xe2x80x83xe2x80x83(IV)
wherein Xxe2x80x2 is chloro, bromo or iodo; and Rxe2x80x3 is selected from C1-12 alkyl, C1-6 alkyl substituted aromatic and phenyl group or two Rxe2x80x3 can be covalently bonded to each other to form a cyclic compound where each Rxe2x80x3 is independently selected therefrom.
The catalyst can also be represented by the following formula V,
Xxe2x80x2Rxe2x80x33P-Y-PRxe2x80x33Xxe2x80x2xe2x80x83xe2x80x83(V)
wherein Xxe2x80x2 and Rxe2x80x3 are defined as above; and Y can be C1-12 alkyl or aromatic group optionally containing alkyls.
The above catalysts can be used in an immobilized form on a silicon resin, silica, inorganic supporter or organic polymer.
The catalysts represented by formula IV and V used in this invention may be benzyltributylphosphonium chloride, tetrabutylphosphonium chloride, tetramethylphosphonium chloride, tetraethylphosphonium chloride, benzyltriphenylphosphonium chloride, ethylene bis(benzyldimethylphosphonium chloride), or immobilized quarternary phosphonium chloride on silica, silicone resin, inorganic supporter or organic polymer.